This invention relates to electromagnetic transducers and particularly to a novel and improved humbucking pickup for stringed instruments such as guitars or the like having ferromagnetic strings.
Electromagnetic pickups function by introducing a magnetic flux path to the metallic strings of the musical instrument and sensing the flux variation produced by string vibrations with a sensing coil also located in the flux path. In most instances, the sensing coils are wound around an array of small cylindrical permanent magnets or magnetic pole pieces, one underlying each of the instrument strings for directing the flux to its respective string.
Unfortunately sensing coils of such pickups are sensitive to interference caused by radiating electromagnetic generating sources such as fluorescent fixtures, transformers, motors, or the like, so that the sensing coils will generate a very disturbing hum signal at a frequency corresponding to the operating frequency of the radiating sources. This problem has led to the development of many types and designs of the so-called humbucking pickups, such as outlined and described in U.S. Pat. No. 4,220,069. In general, all such humbucking pickups comprise at least two identical, conventional or non-humbucking pickups in spaced, parallel locations beneath the instrument strings. The polarity of the flux-producing permanent magnet in each pickup is generally reversed from that in its adjacent pickup and the sensing coils are connected to that signals derived from variations in the flux through the instrument strings are additive in each of the spaced pickups, while signals from extraneous electromagnetic sources are subtractive and tend to buck and cancel the hum voltage generated in the adjacent pickup coil.
Humbucking pickups of this type are usually very sensitive to flux variations due to string vibrations and are also very effective at canceling or bucking out the undesirable hum signals providing that the source of such interfering radiation is at a point substantially normal to the plane of the instrument strings so that the A.C. hum is induced substantially equally in each of the identical sensing coils of the spaced parallel pickups. Coils of the type used for pickup sensing function in a manner similar to direction finders or loop antennae and any imbalance between the two side legs of one coil, or the output of the conventional humbucking configuration of two coils wound in opposition, will result in an A.C. hum output signal which is most undesirable in music pickups.